Assessment of influenza virus exposure and recovery from contaminated surgical masks and N95 respirators
Introduction
Genetic and environmental factors are constantly influencing the transmissibility and infectivity of influenza viruses. As a result, millions of people worldwide are at risk of developing an acute viral infection, and seasonal epidemics as well as global pandemics continue to cause significant morbidity and mortality. The CDC estimates that 9.2–35.6 million influenza illnesses and 12,000–15,000 deaths in the United States have occurred annually since 2010 (CDC, 2017. While vaccination is considered one of the first lines of defense against influenza virus, vaccines may not be immediately available during an outbreak of a novel influenza virus. A better understanding of influenza exposure and transmission is needed to determine the best interventions to avoid the spread of this virus.
Current literature shows that transmission occurs through direct and indirect contact with infectious respiratory secretions (Brankston et al., 2007; Killingley and Nguyen-Van-Tam, 2013; Tellier, 2009; Weber and Stilianakis, 2008) and growing experimental evidence indicates that influenza viruses are transmitted through airborne respiratory particles (Bischoff et al., 2013; Blachere et al., 2009; Lednicky and Loeb, 2013; Leung et al., 2016; Lindsley et al., 2010a; Thompson et al., 2013; Tseng et al., 2010; Yang et al., 2011). Engineering and administrative controls are important in mitigating the spread of infectious diseases. However, transmission-based precautions such as hand washing and the use of personal protective equipment (PPE) including gloves, gowns and masks, also play a major role in protecting healthcare workers and preventing healthcare-associated infections. Although respiratory PPE greatly limits exposure to airborne particles, recommendations for PPE usage vary and depend on the application. To reduce exposure to seasonal influenza, the Centers for Disease Control and Prevention (CDC) recommends that HCWs wear SMs during routine patient care and respiratory protection such as N95 respirators while performing aerosol-generating procedures (CDC, 2009). Surgical masks offer limited protection against infectious bioaerosols, yet effectively protect healthcare workers from contact with large particles and are frequently worn to prevent contamination of sterile environments. In comparison, filtering facepiece respirators such as N95 respirators are designed to filter infectious airborne contaminants but healthcare workers often find them to be less comfortable than facemasks, and they must be fit-tested to ensure effective protection. Several laboratory studies have shown that N95 respirators are nearly completely effective at blocking infectious influenza bioaerosols but SMs are not (Bischoff et al., 2013; Harnish et al., 2013; Janssen et al., 2013; Makison Booth et al., 2013; Noti et al., 2012).
Studies investigating the incidence of influenza among HCWs suggest that healthcare employees are at high risk for exposure particularly during an influenza pandemic (Kuster et al., 2011; OSHA, 2015; Peterson et al., 2016; Santos et al., 2010; Wise et al., 2011). Given the elevated demand for HCWs during a pandemic, in 2011 NIOSH initiated a 5-year multidisciplinary study entitled “Why Healthcare Staff Catch the Flu” (WHSCF) to improve our understanding of how influenza is transmitted including the potential for both aerosol and contact transmission routes. To monitor exposure to influenza aerosols within healthcare settings, studies have used stationary or personal aerosol samplers (Bischoff et al., 2013; Blachere et al., 2009; Lindsley et al., 2010a). Stationary aerosol samplers are usually placed in a patient room and the aerosol is collected on a filter over a period of time. Unfortunately with stationary aerosol samplers, sample collection often occurs away from the patient and is not indicative of direct exposure to the healthcare worker. Personal aerosol samplers have been placed on healthcare workers while conducting patient care activities and analyzed for influenza virus. The use of personal aerosol samplers permits the collection of bioaerosols that are more representative of a healthcare employee’s exposure when in close contact with a patient. Nonetheless, personal aerosol samplers can be cumbersome to wear, are expensive to purchase, and are often available for a limited number of study participants. As part of the WHSCF study, PPE from HCWs and aerosol samples from the Johns Hopkins Student Health Facility and the Adult Emergency Department were collected and analyzed for influenza to determine the relationship between levels of airborne influenza virus and PPE contamination. In particular, SMs and N95 respirators were assessed to determine whether these PPE can serve as “personal bioaerosol samplers” to evaluate potential airborne exposure to influenza virus and also determine if contaminated PPE could serve as a source for infectious virus. Surgical masks and respirators are ubiquitous in a healthcare setting during influenza season and may serve as a tool to assess HCW exposure during specific patient encounters and care activities which may increase exposure potential, such as aerosol generating procedures. However, collection and subsequent detection of influenza from PPE can be difficult. Experimental challenges such as the effect of storage conditions on virus infectivity and nucleic acid stability, low virus recovery efficiency from porous PPE materials, and potentially low virus concentrations of virus expected on respirator and masks used in the field are a few of the concerns this study aimed to address. To establish whether contaminated PPE could be used to assess levels of airborne influenza exposure within a healthcare setting, laboratory studies were performed utilizing a previously described aerosol exposure simulation chamber, with coughing and breathing simulators (Lindsley et al., 2013; Noti et al., 2013; Noti et al., 2012). Aerosol samples along with SMs and N95 respirators placed on the breathing simulator, were analyzed to determine the lowest concentration of influenza virus that could be detected both in the air and on respiratory PPE.
Section snippets
Cell and virus stock
Madin-Darby canine kidney (MDCK) cells (ATCC CCL-34) and influenza A(H1N1) strain A/WS/33 (ATCC VR-825) were purchased from the American Type Culture Collection (ATCC, Manassas, VA). Complete growth medium for MDCK cells consisted of Eagle’s Minimum Essential Medium (EMEM) (ATCC) containing 10% fetal bovine serum (Hyclone Laboratories Inc, Logan, UT), 200 units/ml penicillin G, 200 μg/ml streptomycin (Invitrogen, Carlsbad, CA). MDCK cells were incubated at 35 °C in a humidified 5% CO2 incubator
Effects of sample storage on influenza infectivity
To determine how long influenza virus extracted onsite from facemasks into VTM could be stored, VTM was directly inoculated with virus at low, medium and high TCID50 concentrations, and stored at either 4 °C, −20 °C or −80 °C over a period of 18 days. Using qPCR analysis, we found no statistical significance in M1 gene copies regardless of either temperature or length of storage (Fig. 1A–C). At a TCID50 concentration of 106, 104 or 102, the average M1 copy numbers per one mL sample were 4.8 × 10
Discussion
HCWs are at high risk for exposure to influenza during a pandemic, and as such, preparedness is the key to prevention and control of the transmission of influenza. As part of a multi-year study examining the possible routes of influenza transmission in a healthcare setting, our research was aimed to determine whether SMs and N95 respirators could serve as personal bioaerosol samplers for HCWs exposed to influenza during the course of treating patients and explore laboratory methods to recover
Conclusions
Our experimental setting designed to mimic a HCWs potential exposure to influenza virus demonstrated efficient viral extraction and retention of infectivity on contaminated SMs and N95 respirators. Moreover, influenza-contaminated SMs and N95 respirators provide insight into the aerosol exposure risks that HCWs may encounter in real-world settings such as hospitals and patient examination rooms. These results also support previous studies that suggest that virus trapped on the outside of
Acknowledgements
The findings and conclusions in this study are those of the authors and do not necessarily represent the views of National Institute of Occupational Safety and Health. Authors also declare no conflict of interest.
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